As disclosed in Japanese Patent Application Laid-open No. Hei-8-239788, a conventional hydrogen/oxygen generator is incorporated with an electrochemical cell for performing the water electrolysis, which is a main function of the device. The electrochemical cell comprises predetermined sets of solid electrolyte membrane units that are in parallel array with each other. Each of the solid electrolyte membrane units has electrode plates disposed on the opposite sides of a solid electrolyte membrane with forming spaces between them, in which one space forms an anode chamber as an oxygen generating chamber and the opposite space forms a cathode chamber as a hydrogen generating chamber. Each chamber accommodates a porous electric current supplier.
In the case of a bipolar electrochemical cell, applying a DC voltage between the outermost electrode plates of the solid electrolyte membrane units in parallel array with each other allows these electrode plates to respectively act as monopolar electrode plates of anode and cathode, and the electrode plates between the outermost electrode plates to act as bipolar electrode plates, each of which having opposite side surfaces respectively acting as anode and cathode. That is, a space between each solid electrolyte membrane and an anode side of each electrode plate forms an anode chamber, while a space between each solid electrolyte membrane and a cathode side of each electrode plate forms a cathode chamber.
For example, in electrochemical cell 151 illustrated in FIG. 6, reference numeral 152 represents a bipolar electrode plate disposed in the middle of the electrochemical cell (see FIG. 7), and reference numerals 153a and 153b respectively represent end electrode plates, that is, monopolar electrode plates respectively disposed at the opposite ends. Reference numerals 154 and 155 respectively represent solid electrolysis membranes and porous electric current suppliers. Reference numerals 156 represent annular gaskets made of silicone rubber for isolating the porous electric current suppliers 155 from the outside. Reference numerals 157 represent annular protection sheets. Also, reference numerals 158, 158a, 161 and 161a respectively represent an oxygen gas take-out conduit, an oxygen gas distributing passage, a water drainage conduit for the cathode chamber, and a water drainage passage. Although in this Figure, demineralized water feeding conduit 160, demineralized water distributing passage 160a, hydrogen gas take-out conduit 159 and hydrogen gas distributing passage 159a are not illustrated, it will become apparent that they are arranged in a similar manner as the oxygen gas take-out conduit 158 and the oxygen gas distributing passage 158a once reference is also made to FIG. 7. Reference numerals 162 in FIG. 6 respectively represent end plates, which are tightened together at corresponding peripheral edge portions, i.e., gaskets in this Figure by fastening bolts, which pass through the electrode plates and the like, so that the electrochemical cell 151 is assembled.
The porous electric current suppliers are made of a material permeable to gases such as mesh and sintered material, allowing fluid to be freely distributed passing through the side surfaces of those electric current suppliers.
The conventional electrode plate 152 is of a simple, flat plate shape, and made of a thick titanium plate since it is necessary to form the respective fluid passages 158a, 159a, 160a, 161a in the electrode plate 152 and also form gasket seats for these respective passages.
Meanwhile, the conventional electrochemical cell uses electrode plates of the above-mentioned type, which are simply flat-shaped and made of a thick titanium plate. The electrode plates of this type do not possess elasticity, so that the sealing of the oxygen generating chamber and the hydrogen generating chamber against the outside relies on elasticity of gaskets stacked on these electrode plates. Accordingly, when fastening the bolts for assembling the electrochemical cell, it is necessary to fasten them with sufficient tightening force to exert sealing ability of the gaskets. On the other hand, in the conventional electrochemical cell as illustrated in FIG. 6, the gaskets are merely stacked on the electrode plates of a simple, flat plate shape, so that excessive tightening force may cause the gaskets to deform and hence outwardly and inwardly protrude. Such deformation of the gaskets is likely to invite creep. Particularly, since the temperature of the device itself is increased due to heating by the water electrolysis during the operation of the device, the creep of the gaskets tends to be accelerated. Therefore, in order to compensate for the creep, the fastening bolts must be fastened with larger tightening force. However, this larger tightening force may further invite creep, and therefore cause difficulty in pressing on sealing surfaces at a predetermined pressing force.
The oxygen generating chamber and the hydrogen generating chamber respectively have inner pressures increased during the operation of the electrochemical cell due to generated oxygen and hydrogen gases. As described above, in the conventional electrochemical cell, the soft gaskets are merely stacked on the simply flat-shaped electrode plates, so that the gaskets may protrude to the outside subsequent to the increase in inner pressures of the hydrogen and oxygen generating chambers. Accordingly, there poses a problem that the conventional electrochemical cell is unlikely to withstand high-pressure application which involves generation of high-pressure oxygen or hydrogen gas.
The gaskets also have much larger coefficient of thermal expansion than that of other parts. As described above, the conventional electrochemical cell uses the electrode plates made of a thick titanium plate and therefore the electrode plates themselves do not possess the elasticity. As a result, the thermal expansion of the gaskets may invite the increase in the tightening force by the fastening bolts, posing various problems on the electrochemical cell.
Meanwhile, the electrode plates must maintain a good contacting relationship with adjacent porous electric current suppliers, and therefore are required to have opposite side surfaces formed with high flatness and parallelism. However, since the thick titanium plate as described above is usually manufactured by hot rolling, it resultingly has poor flatness and parallelism. This poses the necessity to perform additional flattening operation of the titanium plate before used for the electrode plate.
In this regard, there was proposed an electrode plate that is formed by a plurality of thin metal plates combined together to achieve an equivalent function as the conventional electrode plate (see the official gazette of Japanese Patent Application Laid-open No. 9-263982). However, the use of plurality of metal plates as a single electrode plate causes higher contacting electrical resistance during the operation, and therefore invites increase in supplying voltage required for operation. As a result, there may cause a problem that the energy efficiency during the operation is deteriorated.
The first aspect of the present invention was conceived in light of the problems involved in the conventional technique. Therefore, it is an object of the present invention to provide an electrode plate that is capable of improving the pressure strength, while maintaining a sufficient elasticity. It is another object of the present invention to provide an electrode plate that is capable of maintaining a high sealing effect of a gasket. It is still another object of the present invention to provide an electrochemical cell that has an improved pressure strength, gaskets with highly maintained sealing effect, and is easy to be assembled.
Also, as described in the aforesaid Japanese Patent Application Laid-open No. Hei-8-239788, the conventional hydrogen/oxygen generator is incorporated with an electrochemical cell for performing the water electrolysis, which is a main function of the device. The electrochemical cell is comprised of predetermined sets of solid electrolyte membrane units that are in parallel array with each other. The solid electrolyte membrane units each have electrode plates disposed on the opposite sides of a solid electrolyte membrane with forming spaces between them, in which one space forms an anode chamber and the opposite space forms a cathode chamber. Each chamber accommodates a porous electric current supplier.
According to a bipolar electrochemical cell, applying a DC voltage between the outermost electrode plates of the solid electrolyte membrane units in parallel array with each other allows these electrode plates to respectively act as monopolar electrode plates of anode and cathode, and middle electrode plates to act as bipolar electrode plates each having opposite side surfaces respectively acting as anode and cathode. That is, a space between each solid electrolyte membrane and an anode side of each electrode plate forms an anode chamber, while a space between each solid electrolyte membrane and a cathode side of each electrode plate forms a cathode chamber.
For example, in electrochemical cell 251 illustrated in FIG. 15, reference numeral 252 represents a bipolar electrode plate disposed in the middle portion of the electrochemical cell (see FIG. 16), and reference numerals 253a and 253b respectively represent end electrode plates (monopolar electrode plates) respectively disposed at the opposite ends. Reference numerals 254 and 255 respectively represent solid electrolysis membranes and porous electric current suppliers. Reference numerals 256 represent annular gaskets made of silicone rubber for isolating the porous electric current suppliers 255 from the outside. Reference numerals 257 represent annular protection sheets. Also, reference numerals 258, 258a, 261, and 261a respectively represent an oxygen gas take-out conduit, an oxygen gas distributing passage, a water drainage conduit for the cathode chamber and a water drainage passage. Although in FIG. 15, demineralized water feeding conduit 260, demineralized water distributing passage 260a, hydrogen gas take-out conduit 259 and hydrogen gas distributing passage 259a are not illustrated, it will become apparent that they are arranged in a similar manner as the oxygen gas take-out conduit 258 and the oxygen gas distributing passage 258a once reference is also made to FIG. 16.
The method of forming the respective conduits and passages will be appreciated once reference is also made to FIG. 17(a) illustrating a part of the electrode plate 252 in cross section. That is, near the peripheral edge of the electrode plate 252 is formed a stepped shallow groove 262 that radially extends, forming an oval shape. FIG. 17(b) is a view as viewed from the line of XVII—XVII in FIG. 17(a). Shoulder portion 262a of the stepped groove 262 is a substrate seat on which oval-shaped substrate 263 is mounted (hereinafter referred to substrate platform 262a). Thus, an oval shaped passage (represented by the hydrogen gas distributing passage 259a) is formed. This substrate 263 forms hydrogen gas take-out conduit 264 in a similar manner at a position corresponding to the hydrogen gas take-out conduit 259. Hydrogen gas introducing hole 264b for connection between the cathode chamber (space filled with the porous electric current supplier) and the hydrogen gas distributing passage 259a are formed on a portion closer to the center of the electrode plate 252 than the hydrogen gas take-out conduit 264. FIG. 17 also illustrates the porous electric current supplier 255, the gasket 256 and the protection sheet 257. In FIG. 17, although the hydrogen gas distributing passage 259a is illustrated as an example, the oxygen gas distributing passage 258a and the demineralized water distributing-passage 260a each have the same structure as that of the passage 259a except for their formed positions.
In FIG. 15, reference numerals 265 represent end plates, which are tightened together via fastening bolts (not shown) passing through the peripheral edge portions of the electrode plates and the gaskets, so that the electrochemical cell 251 is assembled.
The porous electric current suppliers 255 are made of a material permeable to gases such as mesh and sintered material, allowing fluid to be freely distributed passing through the side surfaces of those electric current suppliers 255.
Meanwhile, in the conventional technique, the anode chamber, the cathode chamber and the respective fluid passages are sealed against the outside by the flat plate gaskets 256 which are stacked on flat surfaces of the flat electrode plates (see FIG. 15). Accordingly, in the conventional technique, the gaskets must possess a predetermined elasticity.
On the other hand, during water electrolysis operation, protons are transferred in each solid electrolyte membrane, which is accordingly strongly acid. Therefore, portions to contact the solid electrolyte membrane are required to possess acid resisting property.
To produce a predetermined elasticity according to the conventional technique, a measure was taken along with the use of gaskets made of silicone rubber as the gaskets 256, preventing the gaskets from directly contacting the solid electrolyte membrane and hence preventing oxidation and corrosion of the silicone-rubber-made gaskets by placing thin annular protection sheets made of PFA (perfluoroalkoxy vinyl ether) or the like between the solid electrolyte membrane and the gaskets.
However, even the insertion of the protection sheets may cause fluid leakage if the protection sheets wrinkled or folded. To avoid this, a conventional measure necessitates selection and adoption of high-grade PFA protection sheets free of wrinkle or fold, and assembling by careful attention so as to cause no wrinkle or fold of the protection sheets. This poses a problem of increasing works and costs involved.
On the other hand, there is another option to use thick protection sheets for prevention of fluid leakage therethrough. However, the adoption of the thick protection sheets causes stepped portions between the solid electrolyte membrane and the porous electric current supplier, which may deteriorate the contactability there between and hence invite lowering of the electrolysis efficiency.
Also, in order to allow the silicon-made-gaskets to fully exhibit their sealing ability, bolts must be fastened with a predetermined torque in assembling the electrochemical cell. However, tightening force in this arrangement may cause the gaskets to deform as outwardly and inwardly protruding. Such deformation of gaskets was likely to invite creep as well as deterioration of sealing function.
Even if fastening was achieved with a proper torque in the assembling, there still remains a possibility that the gaskets protrude to the outside due to pressure caused by a generated gas. Therefore, the conventional electrochemical cell was not suitable for the application necessitating the generation of a high pressure gas.
Also, the silicone-made gaskets have much larger coefficient of thermal expansion than that of other parts. Accordingly, they increase in size during use, inviting increase in the fastening force by the bolts and hence posing various problems.
The second aspect of the present invention was conceived in light of the problems involved in the above conventional technique. Therefore, it is an object of the present invention to provide an electrochemical cell that is capable of omitting the use of conventional gaskets or protection sheets, thereby achieving improved sealability, ease of assembling, reduced number of parts, and reduction of thermal expansion due to temperature increase.
As described above, as the electrochemical cell constituting the hydrogen/oxygen generator of the conventional technique, for example, a technique as disclosed in, for example, Japanese Patent Application Laid-open No. Hei-8-239788 is known.
The electrochemical cell according to the conventional technique is comprised of predetermined sets of solid electrolyte membrane units that are in parallel array with each other. The solid electrolyte membrane units each have electrode plates disposed on the opposite sides of a solid electrolyte membrane. In each of these solid electrolyte membrane units, a space between an anode plate and the solid electrolyte membrane forms an anode chamber as an oxygen generating chamber and a space between a cathode plate and the solid electrolyte membrane forms a cathode chamber as a hydrogen generating chamber. Each chamber accommodates a porous electric current supplier.
According to the electrochemical cell made up by using a bipolar electrode, applying a DC voltage to the outermost electrode plates of the solid electrolyte membrane units in parallel array with each other (i.e., the opposite ends of the electrochemical cell ) allows these electrode plates to respectively act as monopolar electrode plates (anode and cathode), and an electrode plate at the midpoint of the electrochemical cell (midpoint between the monopolar electrode plates) to act as a bipolar electrode plate. Herein, the bipolar electrode plate is meant to be an electrode plate having opposite side surfaces respectively acting as anode and cathode. According to this arrangement, a space between an anode side of each electrode plate and each solid electrolyte membrane forms an anode chamber as an oxygen gas generating chamber, while a space between a cathode side of each electrode plate and each solid electrolyte membrane forms a cathode chamber as a hydrogen generating chamber. FIG. 27 illustrates one example of the arrangement of the conventional electrochemical cell. FIG. 28 illustrates a bipolar electrode plate constituting the electrochemical cell as illustrated in FIG. 27.
In electrochemical cell 451 as illustrated in FIG. 27, bipolar electrode plate 452 is disposed between monopolar electrode plates 453a and 453b. Between the monopolar electrode plates 453a, 453b and the bipolar electrode plate 452 are disposed solid electrolyte membranes 454, porous electric current suppliers 455, annular gaskets 456 made of silicone rubber for isolating the porous electric current suppliers from the outside, annular protection sheets 457 and the like. Specifically, the porous electric current suppliers 455 are disposed between the electrode plates 452, 453a, 453b and the solid electrolyte membranes 454, while the annular gaskets 456 are disposed between the electrode plates 452, 453a, 453b and the porous electric current suppliers 455. Also, the annular protection sheets 457 are disposed between the porous electric current suppliers 455 and the solid electrolyte membranes 454.
The bipolar electrode plate 452 forms therein oxygen gas take-out conduit 458, oxygen gas distributing passage 458a, water drainage conduit 461 for the cathode chamber, water drainage passage 461a and the like. Although the omission was made in FIG. 27, it will become apparent that this bipolar electrode plate 452 also forms therein demineralized water feeding conduit 460, demineralized water distributing passage 460a, hydrogen gas take-out conduit 459 and hydrogen gas distributing passage 459a, once reference is also made to FIG. 28.
Referring to FIG. 27, on the outer sides of the respective monopolar electrode plates 453a, 453b (sides opposite to the sides provided with the solid electrolyte membranes 154 and the like) are respectively provided end plates 462, which are fastened and fixed together by fastening bolts or the like extending through the electrode plates 452, 453a, 453b and the like. That is, the electrochemical cell 451 is assembled with the respective components fixed in position with predetermined spacing to each other between the end plates 462, 462 by using a fastening means such as fastening bolts.
The aforementioned porous electric current suppliers 455 are made of a material permeable to gases such as mesh and sintered material, allowing fluid to be freely distributed also passing through the side surfaces of these electric current suppliers 455.
The electrode plates 452, 453a, 453b each form therein passages 458a, 459a, 460a, 461a for the respective fluids. That is, this arrangement necessitates forming gasket seats for these passages 458a, 459a, 460a, 461a, so that the electrode plates 452, 453a, 453b are formed by using a relatively thick titanium plate or the like.
However, the conventional electrode cell has problems as stated below.
That is, the annular gaskets constituting the aforementioned electrochemical cell act as pressure parts for isolating the oxygen generating chamber and the hydrogen generating chamber from the outside of the electrode cell. However, since the annular gaskets themselves are soft, they may be forced out to the outside passing the fastening bolts due to increased inner pressure. Therefore, the electrochemical cell according to the conventional technique is not suitable for high-pressure application.
The annular gaskets also have larger coefficient of thermal expansion than that of other parts. Therefore, there causes large expansion of the annular gaskets during use, resulting in increased fastening forces by the fastening bolts, and hence likely causing various problems on the electrochemical cell. For example, fatigue breakdown or the like may occur on constituent elements of the electrochemical cell.
The electrode plates and other components of the conventional electrode cell are usually exposed to ambient air. Therefore, the electrochemical cell of the conventional technique had a problem of poor weather resistance.
The third aspect of the present invention was conceived in light of the problems involved in the above conventional technique. It is an object of the present invention to provide an electrochemical cell that has made pressure resistance high enough to withstand the high pressure, and is so arranged as to maintain a high sealability between the adjacent components. It is another object of the present invention to provide an electrochemical cell that has improved weather resistance and therefore can be used for a long period of time.
The electrochemical cell according to the conventional technique also has problems as stated below.
That is, in the electrochemical cell so arranged as described above, the bolts as fastening means must be sufficiently tightened for assembling so as to exhibit a proper sealing ability of the annular gaskets. On the other hand, care also has to be taken so as not to fasten the bolts with excessive fastening force and hence protrude the annular gaskets outwardly and inwardly. Also, the operation of the device is accompanied by temperature increase, which causes creep of the annular gaskets and hence lowered sealing effect. Accordingly, additional fastening operation will be needed. However, creep is caused every time the fastening operation is done, and therefore there poses a problem that a sealing surface pressure is hardly maintained at a constant level during the assembling of the electrochemical cell.
In order to improve the electrolysis efficiency, the electrode plates must maintain proper contacting relationship with the adjacent porous electric current suppliers, as well as uniform contacting relationship with the solid electrolyte membranes. These components must be disposed with predetermined spacing from each other so as to have a proper contacting relationship with each other. However, the operation causes thermal expansion and thermal contraction of the electrochemical cell. As a result, it is hard to properly maintain a predetermined distance between the adjacent components for a long period of time.
As described above, it is hard to keep a sealing surface pressure and distance between the adjacent components constant. Particularly, such as uneven surface pressure causes a problem to deteriorate the electrolysis efficiency.
The fourth aspect of the present invention was conceived to address the problems involved in the above conventional technique. It is an object of the present invention to provide an electrochemical cell that is so arranged as to have the respective components of the electrode plate unit and the electrochemical cell substantially equally disposed or contacting surface pressure substantially evenly applied on the whole surfaces thereof, thereby achieving even spacing between the components and even sealing surface pressure, and hence preventing deterioration of the electrolysis efficiency.